The present invention relates to a formaldehyde-free flame retardant treatment for cellulose-containing materials, such as cotton or cotton blends (e.g., cotton/polyester and cotton/nylon), which is durable to both laundering and dry cleaning operations.
There are currently several different types of chemical finishes that can be applied to cellulose-containing materials to impart flame retardant (FR) properties. Of these systems, only a few create finished fabrics that can be laundered and dry-cleaned without losing their FR qualities. These treatments are generally referred to as durable FR finishes. Of these finishes, the most pertinent to the current invention are PROBAN and the PYROVATEX brand materials. The PROBAN technology, from Albright and Wilson, is based on the use of tetrakis-(hydroxymethyl)phosphonium chloride (xe2x80x9cTHPCxe2x80x9d)-based products and an ammoniation chamber. It is described in detail in the following U.S. Pat. Nos. 4,078,101; 4,145,463; 4,311,855 and 4,494,951, all to Albright and Wilson. The PYROVATEX CP methodology, originally developed by Ciba-Geigy, utilizes dimethyl (N-hydroxymethylcarbamoyl-ethyl)phosphonate or a similar methylol-functional phosphorus-containing analogue as the flame retardant agent. Given the market share that PROBAN and PYROVATEX products control in the industry, it is often difficult to understand the widespread tolerance of the negative aspects associated with the use of these products and the various chemistries they employ.
There have been several versions of the THPC cross-linking chemistry used over the years. For example, the precondensate-NH3 process (e.g., PROBAN) technology is the most recent of these versions. Although this may be the most durable treatment on the market, this technology involves the use of an ammoniation chamber and strict application conditions to obtain consistent results without significant strength loss to the fabric. In addition to difficult application conditions, the startup costs for implementing this finishing technique and the regulatory issues associated with ammonia gas make it less than attractive, especially for new arrivals to the market.
In many ways, the PYROVATEX technology suffers from much the same sort of downfalls as the PROBAN technology. Whether it is the original PYROVATEX CP methodology, based on the use of dimethyl (N-hydroxymethylcarbamoyl-ethyl)phosphonate, or other methods using different N-methylol-functional phosphorus-containing analogs, all of the products contain and emit the toxic component formaldehyde (a known carcinogen). In addition to the molecule forming the basis of the PYROVATEX-type approach, a formaldehyde-containing cross-linking resin, such as a N-methylolurea for example, 1,3-dimethylol-4,5-dihydroxyethyleneurea-xe2x80x9cDMDHExe2x80x9d), N-methylolamide, or N-methylolmelamine, is also required to ensure adequate durability of the chemical finish. These resins are also independently used as durable-press cross-linking agents in the textile industry. The combination of a N-methylol phosphorus-containing analog and a N-methylol cross-linking resin, or the use of either reagent separately, often leads to the release of significant amounts of formaldehyde both during fabric application and throughout the lifetime of the garment. As a result, formaldehyde emission levels are limited and closely regulated throughout the industry. The only reason formaldehyde emissions are still tolerated is due to the lack of an acceptable formaldehyde-free replacement technology.
Given the negative impact of formaldehyde on human health, it has been a primary focus of the cotton apparel and textile finishing industries to create equivalent non-formaldehyde technologies. Accounting for their widespread use, most of the current research effort has been spent on the creation and design of new formaldehyde-free cross-linking agents for cellulose-containing materials. These reagents could be used in many different applications, ranging from use in durable-press finishes to general fixation additives for products such as the PYROVATEX-type FR additives. In the past several years, research efforts have led to the discovery of several new low formaldehyde based systems. These finishes are generally based on the structural modification of DMDHEU, either via substitution or elimination of the pendant methylol functionality. Nevertheless, these new finishing agents have never gained widespread acceptance due to their inadequate performance as cross-linking agents. In general, removal or modification of the most reactive aspect of the DMDHEU molecule has only resulted in the generation of less reactive and less desirable finishing agents.
In addition to modifying DMDHEU, other technologies have also begun to develop. One of the more promising non-formaldehyde systems is based on the use of polycarboxylic acids. These molecules create a cross-linked cellulosic material via the in-situ generation of five-membered cyclic anhydrides and their subsequent reaction with hydroxyl moieties contained within the treated textile. This technology was developed at the United States Department of Agriculture in New Orleans under the direction of Clark Welch and was based on the use of 1,2,3,4-butanetetra-carboxylic acid (BTCA). Representative patents describing this approach are: U.S. Pat. Nos. 4,820,307; 4,936,865; 4,975,209; and 5,221,285.
Since the invention of the BTCA technology, additional investigators have begun to work with polycarboxylic acids to improve their commercial attractiveness. Some of the recent work has focused on the use of polymaleic acid and in some cases citric acid or combinations containing citric acid. Polymaleic acid (PMA) is an inexpensive, commercially available material commonly used as a water treatment chemical. Some aspects of this work are described in PCT International Patent Publication No. WO 98/30387. In addition to PMA, there is a wide range of alternative non-formaldehyde cross-linking resins that can be used in creating durable non-formaldehyde FR treatments for cellulose-containing materials. Many of these resins are currently available and used in the water treatment business for scale-inhibition, some of which even contain small amounts of phosphorus. The utilization of these formaldehyde-free, phosphorus-containing resins may even offer additional advantages over the phosphorus-free cross-linking resins such as PMA. Incorporation of phosphorus species into the cross-linking resin itself may eliminate the need for an external cross-linking catalyst and/or the added phosphorus may result in improved FR properties of the treated cellulose-containing materials. Examples of these resins can be seen in the following U.S. Pat. Nos. 4,046,707; 4,105,551; 4,621,127; 5,376,731; 5,386,038; 15 5,496,476; 5,705,475; and 5,866,664.
The present invention relates to an aqueous finishing composition for cellulose-containing materials and the materials treated with such a composition. The aqueous finishing composition, in its broadest embodiment, comprises a hydroxyalkyl-functional organophosphorus flame retardant and a non-formaldehyde cross-linking agent, optionally with a cross-linking catalyst also being included therein.
The aqueous finishing composition, which is intended to be used to treat cellulose-containing materials in accordance with the present invention contains two essential components: (1) a hydroxyalkyl-functional organophosphorus flame retardant (excluding N-methylol, ethers thereof, and potentially formaldehyde releasing reagents); and (2) a non-formaldehyde cross-linking agent.
Monomeric, oligomeric (which generally contain from about two to ten repeat units) and polymeric (which generally contain over about ten repeat units) hydroxyalkyl-functional organophosphorus flame retardant additives are intended for use herein.
A reactive oligomeric phosphorus-containing flame retardant of the type that is described in U.S. Pat. No. 3,695,925 to E. D. Weil and U.S. Pat. Nos. 4,199,534, 4,268,633, and 4,335,178 to R. B. Fearing is an example of one of the hydroxyalkyl-functional organophosphorus flame retardants that can be used in accordance with the present invention. A preferred embodiment has the following structure: 
where R1 is independently selected from methyl and hydroxyethyl, R2is independently selected from methyl, methoxy, and hydroxyethoxy, and n is equal to or greater than 1. This embodiment is made by a multistep process from dimethyl methylphosphonate, phosphorus pentoxide, ethylene glycol, and ethylene oxide and is available under the registered trademark FYROLO(copyright) 51 from Akzo Nobel Chemicals Inc. The endgroups are principally hydroxyl groups.
Another class of materials for use herein includes water soluble oligomeric alkenylphosphonate materials, examples of which are described in U.S. Pat. Nos. 3,855,359 and 4,017,257, both to E. D. Weil. The presence of alkenyl substituents in these materials provide an additional mechanism for permanence utilizing free radical curing conditions (described in the patents above). A preferred species of this type was available under the trademark FYROL(copyright) 76 from Akzo Nobel Chemicals Inc. and is produced by reacting bis(2-chloroethyl) vinylphosphonate and dimethyl methylphosphonate with the substantial elimination of methyl chloride.
Another type of hydroxyalkyl-functional organophosphorus flame retardant that can be employed are oligomeric phosphoric acid esters that carry hydroxyalkoxy groups as described in U.S. Pat. Nos. 2,909,559, 3,099,676, 3,228,998, 3,309,427, 3,472,919, 3,767,732, 3,850,859, 4,244,893, 4,382,042, 4,458,035, 4,697,030, 4,820,854, 4,886,895, 5,117,033, and 5,608,100.
The flame retardant is generally present at from about 1% to about 60%, preferably from about 10% to about 40%, by weight of the aqueous finshing composition.
The non-formaldehyde cross-linking agent, which is the second essential component of the aqueous finishing composition of the present invention, is generally present at from about 1% to about 40%, by weight, of the total weight of that composition, preferably from about 5% to about 20%.
Polycarboxylic acid cross-linking agents form one type of cross-linking agent for use herein. The polycarboxylic acids effective as cellulose cross-linking agents in regard to this invention include aliphatic, alicyclic and aromatic acids either olefinically saturated or unsaturated with at least three and preferably more carboxyl groups per molecule or with two carboxyl groups per molecule if a carbon-carbon double bond is present alpha, beta to one or both carboxyl groups. An additional requirement is that to be reactive in esterifying cellulose hydroxyl groups, a given carboxyl group in an aliphatic or alicyclic polycarboxylic acid should be separated from a second carboxyl group by no less than two carbon atoms and no more than three carbon atoms. In an aromatic acid, a carboxyl group must be ortho to a second carboxyl group if the first carboxyl is to be effective in esterifying cellulosic hydroxyl groups. It appears from these requirements that for a carboxyl group to be reactive, it should be able to form a cyclic 5-or 6-membered anhydride ring with a neighboring carboxyl group in the polycarboxylic acid molecule. Where two carboxyl groups are separated by a carbon-carbon double bond or are both connected to the same ring, the two carboxyl groups should be in the cis configuration relative to each other if they are to interact in this manner. The aliphatic or alicyclic polycarboxylic acid may also contain an oxygen or sulfur atom in the chain or ring to which the carboxyl groups are attached.
In aliphatic acids containing three or more carboxyl groups per molecule, a hydroxyl group attached to a carbon atom alpha to a carboxyl group does not interfere with the esterification and cross-linking of cellulose by the acid. However, the presence of the hydroxyl group may cause a noticeable yellowing of the material during the heat cure. Such an alpha-hydroxy acid is suitable for durable press finishing of suitably dyed cotton fabric, since the color of the dye conceals the discoloration that may be caused by the presence of the hydroxyl group. Fabric discoloration is similarly observed with an unsaturated acid having an olefinic double bond that is not only alpha, beta to one carboxyl group but also beta, gamma to a second carboxyl group.
The discoloration produced in a white cellulose-containing material by cross-linking it with an alpha-hydroxy acid such as citric acid can be removed by impregnating the discolored material with an aqueous solution containing from 0.5% to 5% by weight of a decolorizing agent selected from the group consisting of magnesium monoperoxyphthalate, sodium perborate, sodium tetraborate, boric acid, sodium borohydride, sodium hypochlorite, and hydrogen chloride. The material is immersed in the solution of decolorizing agent and soaked for 5 to 120 minutes at ambient temperature or if necessary in such a solution warmed to a temperature not exceeding 60xc2x0 C. The material is subsequently rinsed with water to remove excess chemicals and solubilized colored products, and then is dried.
A particularly preferred polycarboxylic acid cross-linking agent for use herein is 1,2,3,4-butanetetra-carboxylic acid.
Another preferred polycarboxylic acid cross-linking agent for use herein is polymaleic acid.
Another embodiment for this component is a hydrolyzed terpolymer of maleic anhydride with vinyl acetate and ethyl acrylate. The molar ratio of maleic anhydride to the combined moles of vinyl acetate and ethyl acrylate is preferably from about 2.5:1 to about 5:1 and the molar amount of vinyl acetate to ethyl acrylate is preferably from about 1:4 to about 4:1, most preferably from about 1:2 to about 2:1. The molecular weight of the terpolymer has an upper limit of about 4,000. A product of this type is available under the trademark BELCLENE 283 from FMC Corporation.
Examples of other specific polycarboxylic acids which fall within the scope of this invention are the following: maleic acid; citraconic acid also called methylmaleic acid; citric acid also known as 2-hydroxy-1,2,3-propanetri-carboxylic acid; itaconic acid also called methylenesuccinic acid; tricarballylic acid also known as 1,2,3,-propanetri-carboxylic acid; trans-aconitic acid also known as trans-1-propene-1,2,3-tricarboxylic acid; 1,2,3,4-butanetetra-carboxylic acid; all-cis-1,2,3,4-cyclopentanetetracarboxylic acid; mellitic acid also known as benzenehexacarboxylic acid; oxydisuccinic acid also known as 2,2xe2x80x2-oxybis-(butanedioic acid); thiodisuccinic acid; the phosphorus-containing polycarboxylic acid resins described in U.S. Pat. Nos. 4,046,707; 4,105,551; 4,621,127; 5,376,731; 5,386,038; 5,496,476; 5,705,475; 5,866,664; and the like.
In the event that adequate cross-linking is not accomplished using the previously mentioned systems, it may be necessary to add a suitable cross-linking catalyst to enhance the reaction between the cellulose-containing material which is to be treated, the hydroxyalkyl-functional organophosphorus flame retardant, and the non-formaldehyde cross-linking agent. This catalyst can be present at up to about 30 wt % of the total weight of the aqueous finishing composition, preferably up to about 10%. Examples of suitable catalyst types to select, as set forth in PCT International Patent Publication No. WO 98/30387 and U.S. Pat. Nos. 4,820,307, 4,936,865, 4,975,209, and 5,221,285 include one or more of the alkali metal salts of the known hypophosphite, phosphite, pyrophosphate, dihydrogen phosphate, phosphate, and hydrogen phosphate species, and such acids as one or more of the polyphosphoric, hypophosphorous, phosphorous, and alkyl phosphinic acids. Alternative basic cross-linking catalysts such as NaHCO3 and Na2CO3 can also be used.
In some cases, in order to raise the pH of the treating solution to improve compatibility of the bath or additives and/or for improved strength retention, a portion of the polycarboxylic acid may be used in salt form, especially as a water soluble salt. Suitable for this purpose are alkali metal salts of the acid. Alternatively, or in combination with use of the polycarboxylic acid in salt form, the pH of the treating solution may be raised, or the solution partially neutralized, by the addition of a base, preferably a water soluble base, such as an alkali metal hydroxide, ammonium hydroxide, or an amine. The pH may be elevated for such purpose to about 2.3 to about 5, preferably about 2.5 to 4.